1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine or printer, that can perform an adjustment operation, and an image forming system including a plurality of such image forming apparatuses connected to each other.
2. Description of the Related Art
As a conventional image forming system, a system in which a first image forming apparatus that forms an image on a front side of recording paper and a second image forming apparatus that forms an image on a back side of the recording paper are connected to each other to form images on both sides of the recording paper is known (see, for example, Japanese Patent Application Laid-Open No. 2004-268572).
More specifically, recording paper having an image formed on the front side thereof by the first image forming apparatus is reversed and conveyed to the second image forming apparatus before an image is formed on the back side of the recording paper by the second image forming apparatus.
Some image forming apparatuses perform an adjustment operation such as a gradation correction to stabilize image quality of images output to recording paper. For example, some image forming apparatuses form a pattern image for gradation correction on an intermediate transfer belt to make gradation corrections based on data obtained by reading the pattern image (see, for example, Japanese Patent Application Laid-Open No. 6-148992).
However, if an adjustment operation according to Japanese Patent Application Laid-Open No. 6-148992 should be performed in an image forming apparatus according to Japanese Patent Application Laid-Open No. 2004-268572, it is necessary to perform the adjustment operation at each of adjustment timing of the first image forming apparatus and that of the second image forming apparatus.
An example in which, as illustrated in a specific example of FIG. 7, among 21 periods in all, the adjustment timing is set six times for the first image forming apparatus and five times for the second image forming apparatus will be shown. In this case, if one of the image forming apparatuses performs an adjustment operation, an operation as an image forming system cannot be performed when the image forming system is considered as a whole. Thus, the image forming system stops an image forming operation, causing 10 stop periods in the system as a whole.
Thus, in a conventional image forming system in which a plurality of image forming apparatuses is connected, an image forming operation in the system as a whole is stopped at adjustment timing of each image forming apparatus. Thus, along downtime occurs in the conventional image forming system, resulting in lower productivity.